This invention relates to wireless digital communication systems, and in particular to microcellular packet communication systems.
As personal wireless communication systems such as in cellular telephony proliferate, the spectrum available to the wireless user for accessing cell sites for interactive communication comes at a premium. There is great pressure to shrink the cell size of cellular telephone systems, for example, in order to promote frequency reuse and ultimately increase user density and capacity, as well as to reduce the required transmitter power for battery-operated portables. This is part of the trend toward so-called microcellular systems.
An example of such a microcellular system is U.S. Pat. No. 5,515,369 entitled “Method For Frequency Sharing And Frequency Punchout In Frequency Hopping Communications Network” inventor George Flammer, III, et. al. issued May 7, 1996, (herein “Flammer”) which is herein incorporated by reference. Flammer describes a wireless packet communication system having a plurality of nodes, each having a transmitter and a receiver, the receiver at each node is assigned a seed value and is provided with a channel punchout mask, i.e., channel mask. A node uses its seed value and channel mask to generate a specific randomly ordered channel hopping band plan on which to receive signals. A node transmits its seed value and channel mask to target nodes with which it wants to establish communication links, and those target nodes each use the seed value and channel mask to generate the randomly ordered channel hopping band plan for that node.
As the size of cells decreases and the need for mobility of subscriber units increases, the need for reliable and seamless communication between mobile subscriber units and cell sites increases. In a data communication system such as a wireless mesh network, a subscriber unit moving at a rate of 70 mph would transit cells set on one-quarter mile centers in about 13 seconds. While 13 seconds is adequate time to exchange a substantial amount of data, the acquisition time to establish communication between a subscriber unit and a cell site can frequently exceed 13 seconds. Hence communications between a mobile subscriber unit and a series of cell sites can fail altogether. What is needed is a protocol, which promotes reliable acquisition and communication of mobile subscriber units in a microcellular environment.